Published online by Cambridge University Press: 06 April 2009
1. Out of 57 mice (previously ascertained to have been free from “H. fraterna”) 30 were fed on fresh eggs of Hymenolepis nana, the other 27 serving as controls. Out of the 30 egg-fed mice, only 7 were found to be infected (23·3 per cent.) when examined from thirteen to twenty-six days afterwards. None of the 27 control mice showed infection.
2. This low percentage of infection (when compared with the 90 per cent, infection obtained in my previous work when I fed 20 mice on “H. fraterna” eggs) is probably due to one or more of three factors: (a) change of host (Grassi records that he found it very difficult to infect wild rats with “H. fraterna” eggs obtained from tame rats and in this case the animals were of the same or closely allied species); (b) the full-grown adult condition of the mice; (c) the perfect health of the mice, due to having been supplied with vegetable food (Vitamin B) every day, this condition rendering the mice refractory to infection. In my previous work the mice were in poor condition owing to deficiency of Vitamin B.
3. The proof that rats and mice can be infected with H. nana eggs from Man, the identity of structure of the two parasites and their eggs and their uniform geographical distribution render it practically certain that H. nana and “H. fraterna” are one and the same species. The fact that up to the present there is practically no evidence that Man can be infected with eggs derived from rats or mice does not militate against this conclusion.
4. Mature specimens of H. nana found in tame mice vary enormously in size (as already indicated by Joyeux)—between 7 mm and 80 mm. (measured in balsam) in length. “H. longior” (Baylis, 1922) does not exist as a distinct species.
5. I failed to infect two Cercopithecus monkeys fed with a plentiful supply of fresh H. nana eggs (from Man).
6. Experiments are described which confirm Joyeux's statement that H. diminuta (of the mouse), unlike H. nana, does not possess a direct one-host life-cycle.